1. Field of the Invention
This invention relates to a positive resist composition comprising an alkali-soluble novolak resin in which some hydroxyl group hydrogens are substituted with 1,2-naphthoquinonediazidosulfonyl ester groups and a methyl vinyl ether-monoalkyl maleate copolymer, and a patterning process using the same.
2. Background Art
The recent down-sizing trend of electronic equipment promotes the development of LSIs with higher integration and application-specific ICs, for which multi-pin thin layer bonding is widely employed. In the multi-pin structure, bumps having a height of at least 10 μm are requisite as connection terminals. There is a demand to have a bump forming technique. Photoresist materials are employed when bumps are formed on LSIs by a plating process. Conventional thin film resists are used to form bumps of mushroom shape, which are incompatible with a need to increase the density of LSIs by increasing the number of pins and reducing the pin spacing. It is thus believed necessary that thick film resist be used to form bumps so that the bumps may be shaped to have perpendicular sidewalls (or straight sidewalls). The thick film photoresist for use in the plating step thus has to meet all requirements including high sensitivity, perpendicular geometry, high resolution, and crack resistance during or after the plating step.
Several resist compositions were proposed to solve these problems. JP-A 10-207057 describes a positive photoresist composition in which an acrylic resin is added mainly for the purpose of improving the resistance to plating of bump-forming resist. Also known from JP-B 46-16049 is an alkali-soluble photosensitive resin composition comprising a novolak resin, a naphthoquinonediazide group-containing compound, and polyvinyl ether. Although these resist compositions are successful in improving crack resistance, the pattern shape can be degraded because of a reduced contrast of resist. JP-A 6-202332 discloses a positive photoresist composition comprising a novolak resin and a hydrolyzate of an alkyl vinyl ether/maleic anhydride copolymer having a molecular weight of 20,000 to 80,000. This composition, however, is insufficient in crack resistance during or after the plating step, especially in gold plating application.